The result is null when we execute command "show variables like 'tidb_enable_window_function'" and "show variables like 'tidb_enable_mutation_checker'"';

[sylar8023baby]

Bug Report

1. Minimal reproduce step (Required)

// when we execute command "show variables like ..." ,the result is "Empty set"

mysql> show variables like 'tidb_txn_assertion_level';
Empty set (0.01 sec)

mysql> show variables like '%tidb_enable_mutation_checker%';
Empty set (0.01 sec)

// when we execute command "select @@... , the result is seemd right.

mysql> select @@tidb_txn_assertion_level;
+----------------------------+
| @@tidb_txn_assertion_level |
+----------------------------+
| FAST |
+----------------------------+
1 row in set (0.00 sec)

mysql> select @@tidb_enable_mutation_checker;
+--------------------------------+
| @@tidb_enable_mutation_checker |
+--------------------------------+
| 1 |
+--------------------------------+
1 row in set (0.00 sec)

mysql>

2. What did you expect to see? (Required)

It should return system variables where we are selecting.

3. What did you see instead (Required)

It actully returns "Empty set ".

4. What is your TiDB version? (Required)

// tidb version

mysql> select tidb_version();
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------+
| tidb_version()
|
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------+
| Release Version: v6.0.0
Edition: Community
Git Commit Hash: 36a9810
Git Branch: heads/refs/tags/v6.0.0
UTC Build Time: 2022-03-31 10:33:28
GoVersion: go1.18
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------+

[Defined2014]

I think it's by design. Because TiDBTxnAssertionLevel and TiDBEnableMutationChecker are hidden sysvars. cc @morgo

[morgo]

Yes that's right - it's currently by design. We do have plans to fix it in future though, and no longer hide sysvars. See: https://github.com/pingcap/tidb/blob/master/docs/design/2021-07-29-hidden-sysvars.md

[sylar8023baby]

Thank you

[Defined2014]

It fixed by #35740, so close this issue.